The present invention relates generally to rotary wing aircraft and more particularly to a rotor for such aircraft.
Rotors for use in rotary wing aircraft typically have rotor blades carried at their roots in a rotor head mounted for rotation on the aircraft. Rotors of this kind have connection members attached to the roots of the blades. The connection members are torsionally elastic and usually take the form of a package like collection of tension laminae. The tension laminae of one such package for one pair of rotor blades may be arranged in alternating layers with the laminae of a package for another pair of rotor blades of the same rotor. This layering occurs at the center of the rotor head where the laminae of each package cross over each other. The laminae packages may be centered by means of a pin coaxially arranged relative to the axis of rotation of the rotor. The centrifugal forces which originate in the individual rotor blades about the rotor are therefore counterbalanced at the pin (see for example German DT-PS 15 31 355). When a central support such as a pin is used, however, the laminae package for each rotor blade will twist along its length up to the point of support during each angular movement of the blade. Accordingly, twisting of the tension laminae also occurs at cyclic angular changes of the rotor blades, i.e. in the case of pivot changes of each two diametrically opposed blades in the same direction and by the same amount.
In prior German DT-PS No. 15 31 359, twisting of the laminae in the case of cyclic angular changes of the blades is eliminated in a rotor having only four rotor blades about the rotor by providing endless stretched loops as the tension laminae. The loop connecting one pair of rotor blades is arranged in a vertical plane and the loop connecting the other pair of rotor blades is arranged in a horizontal plane passing through the vertical loop. These loops are arranged so as to pass freely through the center of the rotor head and the dimensions of the loops are chosen such that they will not interfere with each other during cyclic and/or collective angular movements of the rotor blades. When using this type of four-blade rotor, only the collective angular movements of opposite blades will therefore effect twisting of the tension laminae. Thus, torsional stress in the tension laminae can be substantially reduced. In practice, however, it has been found that a central support for each pair of rotor blades about the rotor head is necessary because of imbalances and vibrations which occur in the axial direction of each rotor blade. Therefore, while the above described four-blade rotor may have certain advantages, it has little practical significance.
It is accordingly an object of the present invention to provide a rotor for a rotary wing aircraft which has a central support for each pair of rotor blades about the rotor, but which eliminates the torsional stresses occurring in the torsionally elastic connection member between the rotor blade of a pair of rotors, which result from cyclic angular movements of the rotor blades.
Other objects, features and advantages of the present invention will become more apparent from the description of the invention in connection with the accompanying drawings to be described more fully hereinafter.